Some previously known well service and completion tools and sub-sea devices were designed to operate utilizing application of hydrostatic pressure. In a typical operation, such tools expose one side of a piston or operating rod to an applied hydrostatic pressure upon receipt of a command, while the opposite side of the piston is held at ambient or lesser pressures. A resulting pressure differential causes the piston or operating rod to move (do work), and this motion causes the desired tool or device actuation or deployment.
For example, in a well working tool such as a packer, when the tool is run into the borehole using wireline, coiled tubing or production tubing, an internal piston working in a cylinder with atmospheric pressure maintained upon either end is provided. As the tool is located in a desired position or depth in the borehole, a valve is actuated upon command to expose one side of the piston or operating rod to hydrostatic well pressure. This causes a differential pressure force to be applied to the piston, which, in turn, causes the piston to move. This force and resulting movement are then mechanically translated to perform various sub-surface functions as desired, such as releasing a tool string, setting a packer, opening or closing a valve, or setting a wire line locking and pack off device.
There is need for a safe, small, simple and reliable remotely operated electrically actuated valve for use in tools such as these mentioned above.
In other previously known tools, pyrotechnic and/or explosive operated valves have been utilized. It should be apparent to one of ordinary skill in the art, however, that explosive valves are inherently dangerous in volatile operating environments, and that replacing an explosive valve with a differential pressure valve would provide a much safer device to transport, or use, in a hazardous environment. The lack of pyrotechnic or explosive substances in a valve would also render the device less subject to regulation by governmental agencies and transportation services.
U.S. Pat. No. 6,382,234 to Birckhead et al. and U.S. Pat. No. 5,511,576 to Borland teach a single-use mechanism in which a small piston is held in place by a solid slug of fusible material. The fusible material must have a large enough cross section to support the force on the piston, and its stroke distance is limited to the piston's length. Increasing the length or cross section increases the thermal mass of the material to be fused, which in turn requires more energy to trigger.
However, there are a number of other applications wherein a heat-activated object of fusible material provides an obstacle to the flow of fluid, which is released when the material is melted. High ambient temperatures, rather than a heating element, generally trigger these devices.
For these and other reasons, it would be desirable to have a single-use command activated valve for activating sub-sea or well working tools that is not triggered by random electrical spikes, electrical fields from equipment, or stray ground current on the floor of an offshore platform. Ideally, such a device would be tolerant of high electrical shocks and mechanical vibrations, and be capable of handling varying loads without prematurely triggering.